The objective of this project is a combined biochemical and genetic analysis of the hormonal regulation of plasma membrane phenotype, particularly of those aspects relevant to neoplasia. The glucocorticoid dexamethasone induces a program of membrane changes in rat hepatoma cells (HTC) analogous to the cAMP-mediated reversal of transformed phenotype reported in Chinese hamster ovary cells. The well-characterized hormonal responsiveness of HTC cells makes them a suitable experimental model for studying the hormonal regulation of membrane properties. I will investigate the mechanisms by which glucocorticoids, insulin, and macromolecular serum factors modulate amino acid transport, protease production, intercellular adhesion, cell surface morphology, and the pattern of newly synthesized membrane proteins in HTC cells; and the ways in which these regulatory programs are interrelated. A major goal of this work is the isolation of variant cell lines with lesions in specific hormone-inducible functions. I have already demonstrated the feasibility of isolating HTC cell lines resistant to the dexamethasone inhibition of plasminogen activator production. These variants should provide a powerful tool for studying both the role of proteases in the regulation of membrane phenotype, and the mechanism by which glucocorticoids regulate protease production. I plan to isolate and characterize other variant cell lines resistant to the hormonal regulation of selected membrane properties such as adhesion, amino acid transport, and proteases production in both HTC and CHO cells. Biochemical and genetic analysis of such variants should improve our understanding of the mechanisms of hormonal regulation of membrane phenotype.